This application claims the benefit of priority based on German Application No. 199 57 549.5, filed 30, Nov. 1999, which is incorporated by reference herein in its entirety.
The invention relates to an anti-theft protection system for a motor vehicle, and to a method for operating an anti-theft protection system. The system and the method allow access to (e.g., via a closure system), and use of (e.g., via an immobilizer), a motor vehicle only when authorization is verified.
It is believed that electronic, generally radio-based, closure systems are increasingly replacing conventional mechanical closure systems. It is believed that examples of such radio-based closure systems comprise a code transmitter (e.g., an electronic key, ID transmitter, or ID tag) and at least one transmitting and receiving unit in the motor vehicle. It is believed that examples of such code transmitter have a transponder that contains an electronic code, which is interrogated via radio transmission by one or more of the transmitting and receiving units.
It is believed that various non-contact types of transmission are currently in general use in motor vehicle technology. It is believed that examples of low-frequency systems, e.g., in the 125 kHz frequency band, transmit and receive signals via coils. It is also believed that there are high-frequency systems, e.g. at 433 MHz or 868 MHz.
It is believed that, in general, microwave systems or radar systems can be used for transmitting signals. It is believed that these signals can be modulated with a broad bandwidth such that range or distance can be measured using the radar principle. It is further believed that when using microwaves, distance measurements are essentially based on a radar signal being transmitted in the direction of the measurement object, being reflected by the object, and being received as a reflected signal after a delay time. It is believed that the distance to the object, or changes in that distance, can be deduced by evaluating the phase or time difference between the transmitted signal and the received signal. In addition to pulse delay-time measurement, it is believed that frequency-modulation (FM) or correlation methods can also be used for distance measurement. The general radar measurement principles are described, for example, in J. Detlevsen xe2x80x9cRadartechnikxe2x80x9d [Radar technology], Springer-Verlag, Berlin, 1989.
When such radio frequency (RF) transmission methods are used for transmitting remote-control signals to closure systems or anti-theft protection systems for motor vehicles, it is believed to be important to know the location of the code transmitter in order to satisfy all the security and convenience requirements. In particular, it is believed that knowing whether the code transmitter is located inside or outside the motor vehicle is important in terms of whether the doors are intended to be unlocked or the immobilizer disabled
It is believed that one possibility for interior/exterior detection is evaluating the mean transmitted power of the radio signals. It is believed that this can be done quite well in low-frequency systems, but involves considerable complexity in terms of antenna design and antenna placement, and, frequently, special adaptations to different motor vehicle types. Also, the system becomes more complex in terms of the increased number of transmitting and receiving units, and in terms of the distance measurement accuracy that is required from these units.
An advantage of the present invention is providing an anti-theft protection system having internal/external discrimination with respect to a motor vehicle. In the motor vehicle, a transmitting and receiving unit can be used to transmit signals and then wait for echo signals. All the received echo signals can be supplied to an evaluation unit that uses profiles of the echo signals to determine the location of the code transmitter. Appropriate features of the motor vehicle, such as a central locking system or an immobilizer, can then be controlled accordingly.
The present invention provides an anti-theft protection system for a motor vehicle. The anti-theft protection system comprises a transmitting and receiving unit adapted to be arranged on the motor vehicle, a code transmitter adapted to be portable with respect to the motor vehicle, and an evaluation unit evaluating an echo signal to determine a position of the code transmitter from an echo profile of the echo signal. The code transmitter transmits the echo signal at least in response to receiving the transmitted signal.
The present invention also provide a method for operating an anti-theft protection system for a motor vehicle. The method comprises transmitting a transmitted signal from a transmitting and receiving unit adapted to be arranged on the motor vehicle, receiving an echo signal transmitted from a code transmitter adapted to be portable with respect to the motor vehicle, and evaluating the echo signals in an evaluation unit adapted to be arranged on the motor vehicle. The evaluating includes determining a position of the code transmitter based on an echo profile of the echo signal.